"I’m trying not to think about podiums or anything. I'm my own competition so I really just want to beat my own personal best; that’s something I’ve been trying to do since the last Melbourne Marathon."

O'Donnell will be weaving and wending her way around the streets of inner Melbourne with more than 36,000 others. This weekend's race is shaping up to be the biggest in the marathon's 42-year history.

About 8500 runners have signed up to take part in the full marathon, including Bonbeach local Darren Croton, who is running in his tenth consecutive Melbourne Marathon.

But this year will be his slowest to date.

The 48-year-old Swinburne University professor was diagnosed in November last year with multiple myeloma, a form of blood cancer.

In August, after his first chemotherapy session, Croton signed up for the marathon to raise funds for the Multiple Myeloma Research Foundation and Myeloma Australia.

Runners make it back to the MCG in an earlier Melbourne Marathon.Credit:Joe Armao

"I had no idea whether it would be physically possible or whether I could even do it or whether I could train for it," says Mr Croton, who will be wearing a team shirt, reading 'Fuelled by Chemo' with his running mates.

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"In some sense it’s out of defiance, I wasn’t going to let this define me. I’m not just going to lay down and 'get better', I’m going to go out and do everything I can for my own sanity."